This invention deals generally with agricultural harvesting machines and more specifically with apparatus for detecting the presence of foreign objects such as stones within the crop material processed by such machines.
The problem of foreign materials within crop material being processed by agricultural harvesting equipment moving across the actual farm fields is well recognized. Magnetic detection systems have been previously patented, such as U.S. Pat. No. 3,964,042 by William L. Garrott, which use magnetically sensitive systems to detect the presence of ferrous material in the crop material and protect the machine from damage.
Acoustically activated detection systems have also been described in U.S. Pat. No. 3,675,660 and U.S. Pat. No. 3,805,798, both by Girodat. These acoustically triggered systems are theoretically capable of detecting both ferrous materials and non-ferrous materials, such as stones, but have severe limitations in that they respond to noise created by the mechanical operation of the machine itself. Such spurious responses cause undesirable stoppages in the harvesting procedure, and considerable effort has been directed to their elimination.
Typically, the approach has been to electronically discriminate the types of noises caused by actual foreign objects from the type caused by the machinery, by the use of electronic filtering or comparator circuits, but such methods have never proved completely satisfactory, possibly because the actual characteristics of spurious sounds is so unpredictable that the choice seems to be in accepting false indications or missing true ones.
The foregoing illustrates limitations of the known prior art. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations as set forth above.
Accordingly, a suitable alternative is to provide a sensor in an area of the machine which is itself already acoustically isolated or can easily be isolated, from machine and externally generated noise.